Hindley worm gear



Sept. 8, 1931. s. I. CONE HINIIDLEY WORMYGEAR 4- Sheets-Sheet 1 Filed June 2%, 1925 Patented Sept. 8, 1931 UNITED STATES PATENT OFFICE SAMUEL I. CONE, OF PORTSMOUTH, VIRGINIA, ASSIGNOR TO CONE GEARING CORPORA- TION, OF NORFOLK, VIRGINIA, A CORPORATION OF VIRGINIA nmnLEY wonm GEAR Application filed June 27,1925. Serial No. 40,113. v

This invention relates. to an improved Hindley Worm gear.

Objects of the present invention are to provide a worm of the hourglass or Hindley type and a mating wheel, having'thread and teeth both formed in accordance with principles of design which are of suchchara'cter as to lend themselves to the application of definite co-ordina'ting mechanical processes 10. which,,wh'en solely employed, resultin the production of-parts possessed of ideal intermeshing qualities; toprovide a design 'of worm and wheel in'which there exists a certain precision of mating between the thread and teeth throughout the length of the worm,

' dinary or straight worm, the former embodying modifications of form which'increase its capacity of close intermeshing'with the wheel teeth'and'by which it overcomes to a. great extent the very natural defect existing in the use of the straight worm due to the concentration of the transmitted load, 'These modifications of form'embra'ced in the hourglass type of worm result also injchanging the character of the working contact between the thread and the Wheel teeth which in the use of the straight 0 worm partakes of both-rolling and sliding qualities While in that of the hourglass worm asliding quality alone exists. It is, there-.

- fore, apparent that a worm of the hourglass type and its mating wheel, a combination though only approximately formed as'heretofore produced, may possess advantages over a system in which the worm is straight.

p The object of the presentinvention is, there'- -fore, to so provide an hourglass worm thread and its mating wheel teeth that the assembled the principles being simple and such that theaxes or rotation.-

parts will show precision of engagement when taken through the axial section and will result in the minimum departure from surface contact'when taken above or below said section,

those skilled in the art'may definitely apply them in producing the parts, thus eliminating the practice of second cutting or grinding and the resulting uncertainty of contact value.

It will be understood that in order to provide the intimate mating qualities set forth I herein, it is essential during the fiankfinishing operation in connection with forming 'each member to have the cutting edges of the 'tools follow the natural conformity, respective'ly, of the thread flank of the worm and the tooth flank 0f the wheel in its passage through the other member. Otherwise stated, the cutting action of the tools in .producing'each member must conform substantially to the action of wear which would take place when the finished parts are operated in service. It will, therefore, become apparent that the time relationship and center distance between the axes of rotation must be in accordance with the actual working con ditions.

The said conditions may be fulfilled by rotating a work blank and cutter about axes perpendicular to each other-in the predetermined timed relation and having the said blank and cutter asume relative positions as in service, including the working center dis-v tance between the axes of rotation and then 5 cutting the threads on the worm, or teeth on the wheel, by means of end cutting tools radiated out during the cutting operation, while maintaining a fixed distance between the cen-' ter of rotation; or by edge or side cutting 90 tools made thinner than the required tooth or thread gap and the feed required to pro duce the correctform and width of tooth and thread gap bein accomplished by a. 7 change in the relative position of the cutter and work blank, byishiftifigeither member angularly aboutfitsoWn axis while maintaining the proper timed and position relationship, including fixed 'distancesbetween It will be understood that in cutting the worm threads, that so-called fly cutters will produce the required form, regardless of'the helix angle or ratio selected, and that additional cutters are employed where more rapid cutting is desired. The production of the worm wheel presents a different problem, in that whereas small helix angles and large ratios may be cut substantially correct by the width of the. tooth at the entering end of the worm, gradually reducing in width as the leaving end of the worm thread is approached. This definite surface contact, which is the maximum amount that can be obtained, is brought about and produced not I only by the particular method or process of generating the worm and wheel but also by the relation which exists between the teeth of the worm wheel and the maximum length of the worm. The teeth of the gear wheel arefof a peculiar twisted shape in order accurately' to fit and receive the thread on the worm. The length of the worm is limited to the diameter of the circle described about the I center axis of 'the worm wheel, which circle is such that the flanks of the gear teeth taken in an axial sectionthrough the mid-plane would, if produced, be tangent thereto. -Although the worm could be shorter in length than the diameter of this circle, yet, if it were made shorter, a considerable amount of the bearing surface at the outer. end of the worm would be lost. since this surface hearing is greatest at the entering end of the worm. Therefore, this. particular relatlon produces the maximum amount of surface contact which it is possible to obtain.

'In the accompanying drawings: Fig. 1 is a side elevation of my improved Hindley gear with a detail view of a portion of the worm wheel in position to intermesh therewith;

Fig. 2 is an enlarged side elevation of one portion of the thread projection on the worm Fig. 3 is an enlarged side elevation of a portion of the gear wheel for receiving the thread projection on the worm;

Fig. 4 is a sectional view on the lines E+E+ of Figs. 2,3, and 16;

Fig. 5 is a similar View on the lines D+D of Figs. 2,3, and 16;

Fig. i is a similar View on the lines C+'C+ of Figs. 2, 3, and 16;

Fig. 7 is a similar view on the lines B+B'+ ofFigs. 2-,3,'and16; v

Fig. 8 is a similar view on the lines A+-A+ of Figs. 2,3, and 16;

Fi 9 is a similar view on the lines 70 O- of Figs. 2, 3, and 16; or at the midplane of the worm and wheel;

Fig. 10 is a similar view on the lines A-A of Figs. 2, 3, and 16;

Fig. 11 is a similar view on the lines BB- of Figs. 2,3, and 16;

Fig. 12 is a similar view on the lines C-C of Figs. 2, 3, and 16;

Fig. 13 is a similar view on the line s D-D of Figs. 2, 3, and 16 Fig. 14 is a similar view on the lines E -E of Figs. 2, 3, and 16; i i V Fig. is an expanded diagrammatic view of the contact between the gear teeth and the thread of the worm, taken on sectional lines :v-a: of Figs. 4 to 14, inclusive, and Fig. 16.

Fig. Kids a diagrammatic view on the plane of the gear axis showing the relation between the worm and worm wheel when intermeshed;

tion of the worm and wheel intermeshed.

It is universally admitted that the ordinary type of Hindley worm gear, having several teeth of the wheel in mesh with the worm -!5 thread, though with only a line contact, is greatly superior to the straight type of worm gear in which the whole load is carried on one or two teeth and with onl a point contact at that, due to the form 0 the teeth and 5 the rolling action between the surfaces. This straight worm gear necessarily has a high concentrated unit stress on the contact points, which in the ordinary Hindley gear is distributed over the line contacts of the several teethvin mesh.

This invention provides an im roved Hindley gear in which this load is rther distributed over an equal number of surfaces, which extend not only across the en- 1'19 tire depth of all of the teeth in mesh but also substantially across the width of the tooth at the entering end of the worm, gradually reducing in width as the leaving end of the worm is approached. The surface bearings or contacts of this improved Hindley gear are as superior to the contacts of the ordinary. Hindley gear as the latter are to the contacts of the straight worm-gear. It has been established that this improved Hindley gear gives the maximum surface contact between the thread of the worm and the teeth of the wheel.

Referring to Figsjl and 3, of the drawings, the numeral 1 indicates a gear wheel having the teeth 2 formed on the periphery thereof.

The outer ends of the teeth 2 are concaved as at 3 suiiiclently as shown in Figs. 1, 3, and 16, to receive and roperly fit the intermeshing worm gear. T e space 4 between the'flanks Fig. 17 is a side elevation partly in'sec V length is used.

of the teeth 2 is also concaved as at 6 to properly receive and fit over corresponding and intermeshing portions of the worm thread. As will ap ear in the developments Figs. 3 and 4, the anks of the teeth are reversely curved which define thread gaps with reverse flares. In short, a top view of the teeth with flanks so formed gives the impression of the letter 8. i The worm 7 is provided with a thread 8 as. shown in Figs. land 2 adapted to be received and fitclosely withinthe recessed portion 6 of said wheel, the sides 9 of said thread 8 being adapted to wipe across the flanks 5' of the teeth 2.- The thread 8 on the worm 7 is shownas having five turns about the core 10 p of said worm and, as such, would mesh with five of the teeth on the worm wheel 1. The thread 8 is adapted to engage teeth on the worm wheel 1 throughout the length of the worm, and the length of the worm and the corresponding number of teeth to be engaged ma be varied as desired.

n Fig. 17, the fianks5 of the teeth 2 at the axial section arestraight and, if pro'ected through the wheel, passwithin equa distances from'its center 12 thus becoming tangent to a circle 11 concentric with the center 12. It will be seen that the lines 13 drawn tangent to this circle and parallel to each other when projected across the intermeshing worm will establish its maximum threaded or working length. If this length be exceeded the thread and teeth will become locked, thus preventing the separation of the parts. The working length of the worm may be less than the diameter of the said concentrie circle but the maximum benefits derived from the use of the system are possible only when the limit of This maximum surface contact is revealed by an examination of Fig. 15 in which the contacts between the worm thread and the .teeth are illustrated, the paired lines of the, 5 working faces being shown converg'ng, unit I ing, and diverging respectively. The contacts are thus presented in their most unfavorable aspect since the engagements shown are active across the whole tooth depth. In Figs. 4 to 14 inclusive are shown the Contact or space values at the various levels as O, A+, A etc. Examination of these referring also to Fig. 15 will show the values in both directions as 14, 15, 16, 17 18, 19, 20, 21, 22, 23, and 24. The worm thread, as shown, is left handed and when operated to leftwill create pressure between the alternating pairs ,of contacting surface lines as indicated by the arrows L and in the direction shown. It will be noted that the first pair of lines L representing the entering end of the thread are almost completely coincident while the coincidence of the succeeding pairs is reduced in a uniform order, the final pair representing 55 barely more'than line contact of the thread and tooth. If the drive be reversed in direction the engaging contact will be represented by the pairs of lines marked by and in' the direction of the arrows R, whlch will also represent a reversal of the order of bearing values. Thus, it is shown that the entering end of the worm thread, whichever the direction ofrotation, will possess the greatest surface bearing value, hence the importance of the maximum permissible workin Y length for the worm. The bearing value uctuates to some degree near the entering end of the worm thread due to the position in. rotation of the latter, the minimum occurring immediately before the end of the thread enga es the I tooth and -the maximum immediately a ter. 1

Referring to Fig. 17, it will be seen that the concentric circle 11 subtends the tooth angle in the axial section, its diameter thus being determined by said angle, and since the working length of the worm equals this diameter it follows that the worm length is controlled by the tooth angle.

The sides of the teeth being coincident throughout the axial section with the straight side lines of the worm thread it is evident that the correct thread form may. be gener-" ated on the rotating worm by moving these lines in their fixed relationship to each other,

or a tool with cutting edges corresponding to 9 these lines, about an axis coincident with the axisof the wheel and in the axial section, the desired ratio of movements of observed.

Since the side lines of the teeth must coincide with those of the worm thread inthe axial section, it follows that the principles of formation for both must possess something in common.

Therefore, if the wheel in Fig. 17 be rotated about its axis the sides of its teeth in parts being ice one direction will each in its turn become coincident with the line 13 at one end of the worm, while those of the other sides of the teeth will in turn likewise coincide with the line 13 at the other end of the'worm. Since these lines 13 are parallel to each other and at right angles to the worm axis, it follows that by rotating the generating lines 211, or tdol edges, about an axis coincident with the worm axis in the planes of the lines 13 the proper tooth twist will be generated on, the

rotating wheel, the desirediratio of move- 5 glass typ'e'having threads generated about total load. This uniformity of contact reduces the unit stress and permits a uniform flow of oil to be carried through the teeth,

reducing friction, preventing heating, and decreasing wear, thus lengthening the life of the gear. As a result of the worm and wheel being of exactly the same pitch and in uniform contact, it is evident that the worm and wheel cannot wear out of pitch, remain ing in pitch in both directions until worn out, regardless of the amount of wear or back- For renewing either the worm or wheel of this improved Hindley gear, it is only necessary to know the center distance, pitch, etc. to make either a worm or a wheel which will fit the corresponding wheel or worm that does not need renewing. With the ordinary Hindley gear, both the worm and wheel must be renewed in case either one breaks down or wears out, and needs replacement, each wheel fitting on to the worm with which it was I'nade, and vice versa, and will fit no other part made of different type. As the worm and wheel of my improved Hindley gear arenot ground together and are not dependent on each other for accuracy of fit,

it is not necessary to renew both when only one is worn out. Thus, it will be seen that actual surface .contact is had between the thread of the worm and teeth of the wheel of my improved Hindley gear, which distributes the load over the maximum surface of each of the posed to the nearer line contact which is the most that. itv is possible to ordinary H'indley gear.

I claim: 1. The combination of aworm of the hourobtain with the an axis coincident with that of the mating wheel and in the axial section of the worm; and a mating wheel having the sides of its teeth generated by lines rotating about the worm axis in planes at right angles to the.

worm axis, said planes being two in number and each an equal distance'from the plane -of the wheel axis and in opposing directions therefrom, the same producing surface con 7 tact substantially as described.

2. Gearing comprising worm and worm wheel elements of the hourglass type, the thread of the worm being of constant axial pitch and of length not exceeding the di ameter of a circle described about the center axis of the mating wheel element and such that the flanks of the thread if projected in axial section would be tangent to it, the teeth having reversely curved flanks whereby when the-worm and worm wheel are intermeshed and in relative motion there is afforded more than point or line. contact. I

3. Gearing com rising worm and worm wheel elements 0 the hour lass type, the thread of the worm being '0 constant axial pitch and of length not exceeding the diameter of a base circle described about the center axis of the mating wheel element and I snch that the flanks of the thread if, pr ojected in axial section would be tangent to 1t, the teeth having reversely curved flanks defining thread accommodating spaces'with reverse flares. a

teeth having reversel curved flanks defining thread accommo ating spaces with reverse flares, for the purpose and withcthe result of establishing substantial surface con- 7 tact which is at itsmaximum at the ent'erin end and declines towards the leaving end 0 the worm thread whether the drive be forward orreverse.

5. A gear of the Hindley type, including a worm, and a worm wheel whose flanks when projected in the midplane become .tangent to a circle circumscribed about the axisof the wheel, said flanks having warped surfaces the worm substantiall equaling in length the diameter of said circle and having a constant axial pitch.

6. The combination of a wormof the hourglass type, having threads formed about an axis coincident w1th that of the mating wheel and in the axial section of the worm to provide for constant axial pitch, and a mating wheel having teeth generated in conformity with the'worm thread flanks and whereof the flanks present warped'surfaces formed on re-- versed curves.

7. A system of gearing comprising, in combination, a worm wheel having teeth, the flanks of which are sinuously war d, and Y a worm generated to intermesh t erewith 15 with substantial surface contact.

In testimony whereof I aflix'm signature;

SAMUEL CONE. 

